echo pb-500 backpack blower bogs at full throttle

[JONSSTIHL]

My leaf blower has started giving me trouble lately. It slows down at full throttle


It runs fine until it gets warm, maybe 5-10 minutes then it starts slowing down at full throttle every once in a while until it gets progressively worst and eventually I can't get it to run at full throttle. I can keep it running by letting off the throttle for a few seconds then returning to wot. the problem is intermitent so I can get the job done it just takes longer.


I checked the screen in the exhaust but it wasn't very dirty. I also took the carb off and sprayed it down with carb cleaner. found out it is a strato design and the strato barrel valve in the carb had a bit of oil mix in it so I sprayed everything inside and out with carb cleaner without disassembling it.


I did a search and found out it has reed valves so maybe something is wrong with them but other than the basics I have no clue where to start. The plug is a nice tan color with a little carbon buildup. no obvious fuel leaks, fuel filter is new from last year.

Where do I look next?

 

[CTYank]

My leaf blower has started giving me trouble lately. It slows down at full throttle

Where do I look next?

You tell us nothing about its history, which is important.

Did you try adjusting carb, if that's possible?

Sounds like fuel system. First, change the in-tank filter, and flush out the tank. While there check the fuel line and if squishy or brittle, change it. Could also be tired carb diaphragm(s), which could call for a carb rebuild.

 

[JONSSTIHL]

Sorry, the unit was bought in 2010 and I use it for residential purposes a few times during the summer for debris clean up and then quite intensively for a month in the fall for leaf clean up. I keep the fuel fresh. fuel filter is new and the fuel lines are good. First thing I looked at was to adjust the carb but you know how it is with these new units that they don't want us touching the carbs on. There appears to be two small adjustment screws recessed into small (less that 1/8 inch holes) in the carb body.
they appear to be tiny d head screws but are not labeled H and L.

I've done a little more research and it seems they just need to be tuned but these darn screws make it nearly impossible and the dealer can't sell you the tool.

 

[JONSSTIHL]

the d shape on these screws is tiny, like probably only 1/16 inch in dia. A lot smaller than anything I have ever seen.

 

[nmurph]

Fuel line collapsing, or it has a small hole that is causing it to loose vacuum.

 

[LegDeLimber]

IF my memory serves correctly, the top of the screw is about 2mm or about .080 .
That nylock insert makes 'em a bit of a b**** to get out.
I've got the dimensions somewhere , but between shifting hard drives in the pc and the brain fog
after the knee work, I'm clueless as to where htings are now.

I stumbled across a factory slotted screw that's a repalcement for the little "D" heads.
I pretty well trashed the original ones in getting them out.
It took about 3 months for them to arrive after ordering though.

As far as the running issue, i'd guess the usual tank vent and screen in the carb.
I'd check that new fuel filter too, since it's easy to do.

also these pb-500 s were a bit lean, so i'd check the compression and look in the exhaust
just as a routine to be sure of conditoins of things. plus it's a good time for muffler mod then
while it's removed.

The reed system in them is interesting: there's a pair of petals in the intake block
and then there's one in the port caps at the end of those tubes that wrap around the cylinder.

hopefully I didn't loose the info I had, but I 'll keep looking for the rest of my pics and info.
may take me a littel time..still kinda got a skippy spot in the memory from things.

 

[JONSSTIHL]

Had a little more time today to look into it so I took apart the carb and checked the diaphragm and they looked good, not torn and still flexible. put it all back together and tried it out and it didn't run at wot at all not even cold anymore so I figured I've got nothing to lose. I had kept the original fuel filter when I changed the fuel filter last year so I put the original one back in and low and behold it works.

so plus one for the fuel filter atleast for now. I cut it open and it didn't look all that dirty.

 

[JONSSTIHL]

just a quick update

the fuel filter only worked temporarily the intermittent bog is becoming less and less intermittent.
threw a carb kit in it and cleaned out the carb and a new spark plug and the problem is still there.

I'm really wondering about those reed valves on the side of the cylinder. I wonder what the symptoms of stuck reed valves are.

the new plug did not fix anything and applying the choke doesn't really change anything.

next step is a new fuel line and then it is off to the dealer to file a warranty claim before may 2015,
this pisses me off because the machine has 20 hours on it tops

 

[TIMBERTRON]

did you presure check the carb or have you done a presure and vacuum check on the cylinder and seals and if your just starting to get a leak. and i would check the reed valves they can get stuck from time to time or just break.
what about the muffler port that could be carboned up and cause the unit not to go into full rpms

 

[rmh3481]

Clean out or replace the white 'jelly bean' tank vent. The engine is starving at wot. Pump diaphragm cannot over come the vacuum in the tank.

I usually pull the guts out of the vent and put them back into service.

 

[JONSSTIHL]

forgot to mention in my update that the tank vent is in the cap and is a rubber duckbill setup that is clean. I tried it with the fuel cap off and it still does it. the muffler is clean. It's the first thing I checked. the funny thing is that the choke doesn't seem to affect it. If it was lean I would expect the choke to help it run a little better.

I haven't had time to do a pressure check of the crankcase and the carb was not pressure tested. I just cleaned it out and put the kit in. other than a little bit of corrosion inside the carb there was nothing unusual.

 

[mountainlake]

If there's not enough fuel in the carb for what ever reason the choke won't help. Steve

 

[rmh3481]

If the vent is clear and its still bogging, your going to have to adjust the carb.

Here is a link to the drawings;
http://www.echo-usa.com/documentation.aspx?s=pb-500h&c=en-us

Open the parts diagram, Page 7, Item 15 are the jets.

 

[JONSSTIHL]

when I put the choke on it starts puffing black smoke at idle so it is getting enough fuel at least at idle. I'm reluctant to adjust the carb because when it is running right it is bang on 6800 rpm which is the max rpm spec in the owners manual.

The adjustment screws are micro d head screws so I have to go to the dealer to have access to the tool.

 

[stihl041avhog]

Yes the new epa sucks. You can cut a slot with a dermal tool if you want. It does sounds like the carb needs to be adjusted. Reed valves ? Got to check on that.

 

[mountainlake]

Give the carb a good cleaning. Pay attention to the little inlet screen if it has one. Hows the fuel line? Steve

 

[Saw Dr.]

We have seen several of those with leaking starter side crank seals. The last one, the seal actually came in half. The inner lip/garter spring sheared from the outer portion. I suspect they are not using enough (or any) lube on the seals at the factory.

FYI, Echo will not have the deal in stock (in the unlikely event you can find an actual servicing dealer). Fastenall will show "no stock within 25000 miles of zip code xxxxx", though they can get it. NAPA can get it also, though several days lead time plus shipping.

So what is the realistic fix? I assume you have leaves down, and would rather have it fixed sooner than later....

I have good news. The Stihl 1123 and 1130 series use a seal of the same diameter. You can find a MS 170 carcass at just about every Stihl dealer in existence. I have a couple of straight-gassed MS 250s that I have been scavenging for PB500 seals. Most dealers do not keep lose seals in stock, as the (few) customers who actually want them would prefer to get "fresh" ones when the need arises.

Good luck. Obviously, this is all moot if the piston is scored. We have seen one scored due to that seal failing already this season.

 

[LegDeLimber]

That intermittent bogging getting worse sounds like the way my pb-413 was acting last week.
This was the first usage of the 413 in over a year. Fired it up and after runnig about 2/3 tank of fuel
I began to hear an odd speed drop - bog every 2 or 3 maybe 4 mins.
The blower's second hand , fuel lines are fine and the carb is a known good runner off of the 620 (yes it's a semi-redneck with a blower thing!) So I figured , "ehh probably the duckbill in the cap was another ethanol victim".
Well the faltering went from annoying to dang near wont run over about a 20 min stretch.
Hmm, need to address this little glitch I reckon.
Grabbed a "barely used" fuel filter and gave it a shot of carb cleaner, by back flow through the hose nipple then a very careful light blowout with the air hose.
Looked good enough for now, no ugly color or sticky ,gunky stuff
Fished out the fuel line in the blower tank and swapped in the cleaned filter.
Cranked 'er up and hasn't missed a beat since.

It was so dramatic that when it was done I really wished i had videoed it for a nice little posting about it.

as for the dealers not stocking a crank seal. Sounds sort of sad
considering that seal appears to fit a squatload of different machines.
http://www.ereplacementparts.com/oil-seal-p-520014.html?osCsid=sp495apkammhm39hkpn9fp7ul0

 

[rmh3481]

Great idea on scrounging seals Doc.

Crank Seal Part No Echo 10021300310, two of the same - one on each side. Called just now to see if the seals were available or special order, they are in stock for $5.

Carb was not in stock, $90 at Parts Tree, Echo A021001642. $150 via Walbro - http://wem.walbro.com/walbro/partnumbersearch.asp?ItemNumber=wla&submit1=Go!&ManuItemNumber=

Sounds like you will have to bite the bullet and adjust the carb. Maybe throw the blower in the back of your truck and take it up to the local Echo guy. Hopefully they will fix you up for a $20 tip? Have the plastic cover off so they can get at it when you get there. Im sure they will set it with a tach if its that touchy.

 

[rmh3481]

Echo part number for the adjustment tool on a PB-500H is 91059.

Looks like the Chinese can send new knockoff fully adjustable carbs into the USA by the boxcar w/o a peep out of the EPA, but God forbid an American Citizen tries to buy a Walbro adjustment tool.